In a synchronous PWM control, a switching pattern to control a PWM inverter is calculated. As representative systems that calculate a switching pattern, a system that synchronizes a carrier wave such as a triangular wave with a phase angle of a voltage command (hereinafter, “carrier-wave comparison system”) and a system directly referring to a phase of a voltage command (hereinafter, “phase reference system”) can be exemplified. In these systems, the carrier-wave comparison system can simplify a configuration of a control system and is excellent in the responsiveness to a voltage command, whereas the phase reference system can effectively suppress a higher harmonic component contained in an inverter output voltage. Conventionally, there are many technical literatures about the carrier-wave comparison system. Nonpatent Literatures 1 and 2 and Patent Document 1 mentioned below are representative literatures about the phase reference system.
When a synchronous PWM control is performed, an approximate shape of a switching pattern can be recognized in many cases. This means that, in the synchronous PWM control, the shape of an inverter output voltage can be recognized in advance. Therefore, in the synchronous PWM control, a switching phase can be obtained in advance to be able to obtain desired characteristics of an inverter output-voltage waveform in one cycle of a voltage command.
Nonpatent Literatures 1 and 2 disclose setting methods of a switching phase that make it possible to perform suppression of a higher harmonic component contained in an inverter output voltage and assigning an arbitrary fundamental wave component. Patent Document 1 discloses a setting method of a switching phase in which a fundamental wave component contained in an inverter output-voltage waveform matches a voltage command.
Patent Document 1: Japanese Patent Application Laid-open No. H6-253546
Nonpatent Literature 1: IEEE Transactions On Industry Applications (1973, Vol.IA-9, No. 3), Generalized Techniques of Harmonic Elimination and Voltage Control in Thyristor Inverters Part I-Harmonic Elimination
Nonpatent Literature 2: IEEE Transactions On Industry Applications (1974, Vol. 10, No. 5), Generalized Techniques of Harmonic Elimination and Voltage Control in Thyristor Inverters Part II-Voltage Control Techniques